Optical brighteners compositions their production and their use

ABSTRACT

The invention relates to an optical brightener mixture (W) comprising optical brighteners (A) of formula (Ia), and (B) of formula (Ib) and optionally (C) of formula (Ic) as defined herein, their concentrated aqueous solutions (S), their production and their use.

[0001] In the handling of water soluble optical brighteners it is oftendesired to use pre-formulated concentrated aqueous solutions, e.g. forease of handling and metering. It is also desired to receive suchconcentrated solutions—especially in a storage stable form of a givenstandard concentration—from the supplier, in order to avoidtime-consuming dissolving of dry products, e.g. in the form of powders,in the application plant. Consequently a further requirement for theconcentrated solutions is that they be stable to such conditions as mayoccur during transportation and storage, e.g. frost and heat conditions.In the case of optical brighteners with a limited number of watersolubilizing substituents, in particular sulpho groups, morespecifically optical brighteners of the 4,4′-bis-triazinylamino-stilbenedisulphonic acid series which at each triazinyl ring contain an anilinosubstituent that does not contain any sulpho group as a substituent, andan aliphatic amino radical that contains no sulpho group, theirsolubility may be insufficient for producing concentrated aqueoussolutions, and the corresponding aqueous compositions may then just besuspensions, which need the addition of suspension stabilisingadditives, or if an aqueous concentrate solution can be produced—e.g.with the aid of a substantial proportion of a solubiliser or hydrotropesuch as urea or a polyethyleneglycol—, the stability to storage andtransportation thereof may vary with concentration, especially insofaras at lower concentrations, such as in the range of 15 to 30%, at whichthe solutions are also less viscous and thus easier to handle, thestability of the solutions may even be worse than at higherconcentrations, while the use of substantial proportions of additives,such as urea or polyethyleneglycol, correspondingly increases the burdenin the backwater (as N-content or COD) of the application plant. With aparticular choice of the counter-ions for the sulphonic acid groupsthere may be achieved a certain partial improvement, but the storagestability may still represent a problem, especially under varyingtemperature conditions.

[0002] WO 0046336 A1 discloses an optical brightener mixture of4,4′-bis-(4-sulphophenylamino-6-di-ethanolamino-2-s.triazinylamino)-stilbene-2,2′-disulphonicacid,4,4′-bis-(4-sulphophenylamino-6-diisopropanolamino-2-s.triazinylamino)-stilbene-2,2′-disulphonicacid and the corresponding asymmetrical compound, in triethanolaminesalt form. These compounds contain four strongly water solubilizing,aromatically linked sulphonate groups and in the examples they areproduced in the form of aqueous solutions.

[0003] U.S. Pat. No. 5,518,657 discloses aqueous suspensions of mixturesof optical brighteners of the distilbene-disulphonic acid series and ofthe 4,4′-bistriazinylamino-stilbene-2,2′-disulphonic acid series whichaccording to the generic definition in the specification may contain assubstituents at the available 4- and 6-positions of the triazinylaminoradicals phenylamino and the radical of an aliphatic amine (in thegeneric portion of the specification there are mentioned morpholine,piperidine and amines substituted with C₁₋₄-alkyl, benzyl, cyclohexyl,ethylcyclohexyl, β-hydroxyethyl, β-hydroxypropyl, β-cyanoethyl,2-methoxy- or -ethoxy-ethyl or 3-methoxy-propyl). Of the latterbrighteners there are specifically mentioned in the examples:4,4′-bis-(4-phenylamino-6-morpholino-2-s.triazinylamino)-stilbene-2,2′-disulphonicacid and4,4′-bis-(4-phenylamino-6-ethylamino-2-s.triazinylamino)-stilbene-2,2′-disulphonicacid. These aqueous suspensions of the defined optical brightenermixtures are formulated with electrolytes, an anionic polysaccharide (inthe examples Xanthan) and a dispersant (in the examples an anionicdispersant) for stabilisation.

[0004] It has now surprisingly been found that with a combination of twoparticular groups of optical brighteners of the anilino-substituted4,4′-bis-triazinylamino-stilbene disulphonic acid series with aliphaticamino substitution at the triazinyl rings and with no sulpho group atthe anilino substituent, there may be produced concentrated aqueoussolutions and there may be achieved an unexpectedly satisfactorystability of the aqueous solutions at any concentration even undervarying temperature conditions, while the addition of any solubilisingor stabilising additive may be reduced to a minimum or even be avoidedat all.

[0005] The invention relates to the particular mixture of the belowdefined optical brighteners and certain asymmetrical opticalbrighteners, their concentrated aqueous compositions (in particularsolutions), their production and their use.

[0006] The invention thus firstly provides an optical brightener mixture(W) comprising an optical brightener (A) of formula

[0007] wherein

[0008] R signifies hydrogen or methyl,

[0009] R₁ signifies hydrogen, unsubstituted C₁₋₆-alkyl, C₁₋₆-alkylsubstituted with carbamoyl or carboxy, C₂₋₆-alkyl substituted withhydroxy or methoxy, hydroxy- or methoxy- —(C₂₋₃-alkoxy)-(C₂₋₃-alkyl),

[0010] R₂ signifies C₁₋₆-alkyl substituted with carbamoyl or carboxy,

[0011] or R₁ and R₂ together with the nitrogen to which they are linkedform a carboxypyrrolidine ring,

[0012] and M signifies an equivalent of a cation,

[0013] and an optical brightener (B) of formula

[0014] wherein

[0015] R signifies hydrogen or methyl,

[0016] R₃ signifies hydrogen, unsubstituted C₁₋₆-alkyl, C₂₋₆-alkylsubstituted with hydroxy or methoxy, or hydroxy- ormethoxy-(C₂₋₃-alkoxy)-(C₂₋₃-alkyl),

[0017] R₄ signifies hydrogen, unsubstituted C₁₋₆-alkyl, C₂₋₆-alkylsubstituted with hydroxy or methoxy, or hydroxy- ormethoxy-(C₂₋₃-alkoxy)-(C₂₋₃-alkyl),

[0018] or R₃ and R₄ together with the nitrogen to which they are linkedform a morpholine ring,

[0019] and M signifies an equivalent of a cation.

[0020] If in the above formulae (Ia) or (Ib) R signifies methyl, thismay be in any of the positions ortho, meta or para to the amino group,preferably R signifies hydrogen. If alkyl in any of the significances ofR₁, R₂, R₃ or R₄ contains 3 to 6 carbon atoms it may be linear orbranched; if it contains 6 carbon atoms it may also be cyclic. Among theunsubstituted C₁₋₆-alkyl groups the lower molecular ones are preferred,in particular those with 1 to 3 carbon atoms, namely methyl, ethyl,propyl and isopropyl, especially methyl and ethyl. Among the C₁₋₆-alkylgroups substituted with carbamoyl or carboxy in any of the significancesof R₁ or R₂ the lower molecular ones are preferred, in particular thosewith 1 to 3 carbon atoms in the alkyl radical, namely methyl. ethyl,propyl and isopropyl, especially methyl, ethyl and isopropyl. Among theC₂₋₆-alkyl groups substituted with hydroxy or methoxy the lowermolecular ones are preferred, in particular those with 2 or 3 carbonatoms in the alkyl radical, especially ethyl and isopropyl. In theC₂₋₃-alkyl radicals substituted with hydroxy or methoxy orhydroxy-C₂₋₃-alkoxy or methoxy-C₂₋₃-alkoxy the substituent is preferablyin the β-position.

[0021] R₁ preferably signifies unsubstituted C₁₋₃-alkyl or C₂₋₃-alkylsubstituted with hydroxy. R₂ preferably signifies C₂₋₃-alkyl substitutedwith carboxy or preferably carbamoyl.

[0022] R₃ preferably signifies unsubstituted C₁₋₃-alkyl or C₂₋₃-alkylsubstituted with hydroxy. R₄ preferably signifies unsubstitutedC₁₋₃-alkyl or C₂₋₃-alkyl substituted with hydroxy.

[0023] M may be in general an equivalent of any cation as conventionallypresent in anionic optical brighteners, especially a non-chromophoriccation that favours water solubility of the brightener, in particular analkali metal cation, preferably lithium, sodium or potassium, or anammonium cation, in particular unsubstituted ammonium or ammoniumsubstituted with 1 to 3 low molecular alkyl or hydroxyalkyl groups,preferably C₁₋₄-alkyl and C₂₋₃-hydroxyalkyl, e.g. methyl, ethyl,β-hydroxyethyl and β-hydroxypropyl; among the ammonium cations arepreferred mono-, di- and/or triethanolammonium and mono-, di- and/ortriisopropanolammonium. The cation equivalents M may all be of one kindor may be the equivalents of two or more different cations. According toa particular feature of the invention, the brighteners contain two ormore different cations M, e.g. ammonium and alkali metal cations, orunsubstituted ammonium and substituted ammonium, or alkali metal andsubstituted ammonium cations, or unsubstituted ammonium and alkali metaland substituted ammonium cations, the counter-ions M may preferably be amixture of one or more substituted ammonium cations with an alkali metaland/or unsubstituted ammonium cation. The substituted ammonium cationsare preferably tertiary ammonium cations.

[0024] The above optical brighteners (A) and (B) are known compoundsor/and may be produced by known methods or analogously to known methods,in particular by reaction of cyanuric halide, preferably cyanuricchloride, with the amines of formulae

[0025] in which M′ signifies an alkali metal cation,

[0026] and either

[0027] for producing optical brighteners of formula (Ia),

[0028] or

[0029] for producing optical brighteners of formula (Ib).

[0030] The reaction is in general a dehydrohalogenation and is suitablycarried out under dehydrohalogenating conditions. The sequence of thereactions is in any desired order. The cyanuric halide, preferablycyanuric chloride, is preferably reacted first with the diamine offormula (II), the product is then reacted with the aromatic amine offormula (III) to give an intermediate of formula

[0031] in which Hal signifies halogen, preferably chlorine, which isthen reacted with the aliphatic amine of formula (IV) or (V)respectively

[0032] The mixtures of optical brighteners (A) and (B) may be producedby processes conventional per se, in particular by mixing (A) with (B)optionally in the presence of water or by reacting an intermediateproduct of formula (VI) with amines of formulae (IV) and (V)sequentially or in admixture.

[0033] By the reaction of the intermediate of formula (VI) with theamines of formulae (IV) and (V) sequentially or in admixture there areformed the optical brighteners (A) and (B) of formulae (Ia) and (Ib) inadmixture, and further there is also formed an optical brightener (C) offormula

[0034] components (A), (B) and (C) being in statistical distribution.

[0035] The mixture (W) may thus be a mixture of (A) and (B) or also amixture of (A), (B) and (C).

[0036] The reactions of the halogens of the cyanuric halide with therespective amines take place suitably under dehydrohalogenatingconditions. For substitution of the first halogen of the cyanurichalide, in particular for the reaction with the diamine of formula (11),it is preferred to operate at a temperature in the range of 0 to 20° C.and under distinctly acidic to neutral pH conditions preferably in thepH-range of 1 to 7. For substitution of the second halogen of thecyanuric halide, in particular for producing the intermediate product offormula (VI), it is preferred to operate at a temperature in the rangeof 20 to 60° C. and under weakly acidic to weakly alkaline conditions,preferably at a pH in the range of 4 to 8. For substitution of the thirdhalogen of the cyanuric halide, in particular the reaction of a compoundof formula (VI) with the aliphatic amine of formula (IV) or (V) or withthe amines of formulae (IV) and (V) in admixture or sequentially, it ispreferred to operate at a temperature in the range of 60 to 100° C. orreflux and under weakly acidic to distinctly alkaline conditions,preferably at a pH in the range of 4 to 10, more preferably 7 to 10 Thealiphatic amine is preferably employed in excess over the stoichiometricquantity, e.g. in an excess of >5 mol-%, e.g. in the range of 5-100mol-% preferaby 20 to 80 mol-%. The pH may be controlled by addition ofsuitable bases, preferred bases being those suitable for providing theabove mentioned cations M, e.g. alkali metal (e.g. lithium, sodium orpotassium) hydroxides, carbonates or bicarbonates, ammonia or—for thereaction of the third halogen of cyanuric halide, i.e. for thecondensation of the intermediate of formula (VI) with the aliphaticamines of formula (IV) or (V)—also low molecular tertiary aliphaticamines such as tri-(C₁₋₄-alkyl- or/and C₂₋₃-hydroxyalkyl)-amines, amongwhich tri-ethanol- or -isopropanol-amine, are particularly preferred.

[0037] Where the mixtures (W) are produced by mixing (A) with (B), thesemay be in dry form, e.g. as powders, that are dry-mixed with each other,or in the form of aqueous solutions of each of (A) and (B), which aremixed with each other. Where (W) is a mixture of (A), (B) and (C), it isexpediently produced by the above reaction of the intermediate offormula (VI) with the amines of formulae (IV) and (V) sequentially or inadmixture.

[0038] The molar ratio of the mixture components of (W) may be relatedto the molar ratio of the starting aliphatic amines of formulae (IV) and(V) employed for producing the mixures of (A) and (B) or of (A), (B) and(C). The molar ratio of the amines of formulae (IV) and (V) ispreferably in the range of 10/90 to 90/10, advantageously 25/75 to75/25, preferably 40/60 to 60/40. Thus, if (W) is a mixture of opticalbrighteners (A) and (B) the molar ratio (A)/(B) preferably is in therange of 10/90 to 90/10, advantageously 25/75 to 75/25, preferably 40/60to 60/40. If (W) is a mixture of (A), (B) and (C), their molar ratiowill correspond to the statistical distribution resulting from the useof the mixture of amines of formulae (IV) and (V) in the stated molarratio, i.e. 10/90 to 90/10, advantageously 25/75 to 75/25, preferably40/60 to 60/40.

[0039] In the mixtures (W) the cations in the significance of M arepreferably selected from:

[0040] M₁ alkali metal cations (e.g. lithium, sodium or potassium) andunsubstituted ammonium

[0041] and M₂ ammonium mono-, di- or trisubstituted with C₁₋₄-alkyland/or C₂₋₃-hydroxyalkyl.

[0042] M₁ preferably is an alkali metal cation, more preferably sodium.M₂ preferably is a mono-, di- or tri-(C₂₋₃-hydroxyalkyl)-ammoniumcation, more preferably triethanolammonium. Preferably at least 50 mol-%of M₂ is a tertiary ammonium as described above, more preferablytriethanolammonium

[0043] According to a preferred feature cations M₁ and M₂ are bothpresent as M in the mixture (W).

[0044] The ionic ratio M₁/M₂ is e.g. in the range of 10/90 to 90/10,advantageously 25/75 to 75/25, preferably 40/60 to 60/40.

[0045] The cations M, in particular M₁ and M₂, are suitably chosen insuch a kind and ratio that the optical brightener mixture (W) issufficiently water soluble to give a concentrated aqueous solution, e.g.of a concentration ≧3%. Preferably the (W)-concentration in the aqueous(W)-solution is in the range of 5 to 60%, advantageously 8 to 50%, morepreferably 12 to 40%, especially 15-35% by weight, a typically preferredconcentration range being 20 to 30% by weight.

[0046] The optical brightener mixtures (W) are usually obtained in awater soluble salt form, in which the salt forming cations are asresulting from the synthetic conditions or/and may be replaced e.g. bymethods conventional per se, such as precipitation by acidification(e.g. with strong mineral acids, e.g. hydrochloric, sulphuric,phosphoric or nitric acid) and salt formation with the desired base(e.g. amine) or by treatment with suitable ion exchange resins or acidresins in the presence of an amine. The produced (W)-solutions (S) maycontain some salts, in particular halides, preferably chlorides, of thestated cations, mostly inorganic salts, mainly sodium chloride, asresulting from the dehydrohalogenation reaction and/or optionally othersalts resulting from precipitation with an acid. According to apreferred feature the content of these extraneous electrolytes in the(W)-solution (S) is reduced to a minimum, in particular to less than 5%by weight referred to (W), e.g. in the range of 0.01 to 5%, preferablyto <4%, e.g. in the range of 0.1 to 4%.

[0047] The invention thus also provides an aqueous composition, inparticular solution (S′), of (W), in which the content of extraneouselectrolytes, i.e. other than those involved in salt formation in (A)and (B),—especially of inorganic salts—is less than 5% by weightreferred to the weight of (W).

[0048] This reduction of the content of extraneous electrolytes may beachieved by methods conventional per se in the art or analogously toconventional methods, e.g. by membrane filtration or by acidificationprecipitation, filtration and salt formation by addition of bases, or byseparation in a two-phase system of two liquid phases, one of whichpreferentially dissolves the optical brightener, the otherpreferentially dissolves the above mentioned extraneous electrolytes,mainly sodium chloride. According to a further feature of the process,the above described reaction of the third halogen of cyanuric halide,i.e. the reaction of the compound of formula (VI) with the aliphaticamines of formula (IV) or/and (V), can be carried out in such a twophase system. The above optical brighteners, i.e. (A), (B) or (C) or themixture (W), together with water—preferably in the form of concentratedaqueous solutions (S) of the above mentioned (W) concentrations—andoptionally also together with the above tertiary amines, especiallytriethanolamine or triisopropanolamine, optionally in salt (especiallychloride) form, may form with heating in particular to atemperature >42° C., preferably in the range of 45 to 90° C., a liquidmixture which, on cooling, in particular to a temperature <42° C.,preferably in the range of 10 to 40° C., more preferably 15-38° C.,settles out as an organic phase and may be separated as the lower layerfrom the salt-containing aqueous phase which constitutes the upperlayer. Preferably at least 30 mol-% of the inorganic cations are shiftedand replaced by such tertiary ammonium ions e.g. 30 to 90, preferably 40to 80 mol-%. Where the above reaction of the intermediate of formula(VI) with the aliphatic amine is carried out under such conditions thata two phase system is formed, the aliphatic amines (IV) and (V) arepreferably employed in a larger excess over the stoichiometric quantity,e.g. in an excess of 50-100 mol-% over the stoichiometric quantity.

[0049] The process for the production of these (W)-containingcompositions or solutions (S) with reduced content of extraneouselectrolytes, in particular concentrated aqueous (W)-solutions (S′), isin particular characterized in that

[0050] a) a salt-containing aqueous solution (S″) of (W) is desalinatedby membrane filtration,

[0051] or b) the mixture (W) is precipitated in acid form byacidification of a salt-containing aqueous solution (S″) of (W) with astrong mineral acid (e.g. HCl, H₂SO₄, H₃PO₄, HNO₃), separated, e.g. byfiltration, and redissolved in salt form by reaction with the suitablebase or base mixture,

[0052] or c) the (W)-solution (S″) is treated with an acid ion exchangeresin or acid membrane in the presence of amine as suitable forintroducing M₂,

[0053] or d) the salt-containing mixture (W), preferably in the form ofa salt containing solution (S″), is selectively separated in a system oftwo liquid phases L₁ and L₂, of which L₁ is aqueous and dissolves theextraneous electrolytes and L₂ is organic and contains (W) and maycontain a minor proportion of dissolved water, and the desalinated(W)-containing phase L₂ is separated from the salt-containing aqueousphase L₁. or two or more of the stated process variants a), b), c) andd) are combined.

[0054] The so produced (W)-solutions (S) and especially (S′) may be ofany desired concentration and viscosity, so long as they are stirrableand pourable, e.g. in the range of 50 to 3000 cP at 20° C. Preferredconcentrations for the concentrated aqueous solutions (S) and especially(S′) are, as stated above, at a (W)-concentration e.g. in the range of 5to 60%, advantageously 8 to 50%, more preferably 12 to 40%, especially15-35% by weight.

[0055] If desired there may be added one or more formulation additives(F), which may e.g. be

[0056] (F₁) a stabilising additive,

[0057] (F₂) a defoamer,

[0058] and/or (F₃) an additive for protection against the damagingaction of microorganisms, e.g. a fungicide or a bacterial growthinhibitor.

[0059] As (F₁) there may in particular be employed a water solublesolvent or solubiliser and/or a base, e.g. a hydroxy group-containingaliphatic compound, in particular a glycol (such as a C₂₋₄-alkyleneglycol, diethylene glycol or a polyethylene glycol of average molecularweight {overscore (M)}_(w) up to 1500) or a hydroxyalkyl-substitutedaliphatic amine, such as mono-. di- or tri-ethanol- or-isopropanol-amine, or a trishydroxymethylaminomethane such astrishydroxymethylaminomethane and2,2-bis-(hydroxymethyl)-2,2′,2″-nitrilotriethanol, or also ammonia orother amine such as mentioned above for salt formation. Among these thetertiary alkanolamines, especially those of formula

[0060] in which n Is 0 or 1, preferably 0, are preferred.

[0061] These additives (F₁)—if employed—are suitably employed in anefficient amount, which preferably is at a concentration of up to 5% byweight, referred to the concentrated (W)-solution, in particular in therange of 0.1 to 5% by weight referred to the concentrated (W)-solution.

[0062] According to a preferred feature of the invention the amine fromwhich M₂ derives and any (FI) are the same trialkanolamine, i.e.triisopropanolamine or more preferably triethanolamine, which preferablyis also a component in the organic phase L₂ in desalination processvariant (d), if this is employed. In this way particularly stabledesalinated compositions (S′) can be produced without the addition ofany other (F₁).

[0063] The concentrated solutions (S) of the invention may be of anysuitable pH, e.g. from weakly acidic to distinctly basic, preferablynearly neutral to distinctly basic, and M and any (F₁) are expedientlychosen accordingly, preferably so that an aqueous, 10 weight-% solutionof the optical brightener mixture has a pH in the range of 5 to 10,preferably 7 to 9.5.

[0064] As additives (F₂) or (F₃) there may be employed commerciallyavailable defoamers and antimicrobial additives, and they are suitablyemployed in an efficient amount, which usually is in the rangerecommended for each of the respective commercial products, e.g. at aconcentration of up to 0.2% by weight referred to the concentratedaqueous solution, in particular in the range of 0.001 to 0.2, preferably0.01 to 0.1% by weight referred to the concentrated (W)-solution.

[0065] The (W)-solutions (S) of the invention—especially those in which(W) is at least in part in M₂-salt form, preferably the desalinated ones(S′), most preferably those further containing (F₁) in particular aspreferred above—are of outstanding stability to storage andtransportation, also under varying temperature conditions, such as frostand heat, not only at high concentrations and viscosities, such as 2000cP or above (where they do not crystallize or precipitate even byseeding), but also at lower concentrations and viscosities, such as 50to 1000 cP, (where they are of outstanding stability even when freezingand thawing and/or under heat conditions e.g. up to 50° C.).

[0066] The so produced solutions (S) or (S′) are ready for use and areeasy to handle and meter. If desired the desalinated solutions (S′) maybe dried to powders or granular pourable products (W′).

[0067] The mixtures (W) and their solutions (S) and in particular (S′)according to the invention are suitable as optical brighteners for theoptical brightening of any substrates, which are usually brightenablewith each of the optical brighteners (A) or (B) e.g. in sodium saltform. E.g. for the optical brightening of cellulosic substrates, such astextiles, paper, board and non-wovens, by methods conventional per se.Preferably they are suitable for the optical brightening of paper andpaper board, e.g. in the paper stuff suspension, or after sheetformation, e.g. in the form of paper web simultaneously with theapplication of a size or coating. They are distinguished in particularby their high stability, yield and ease of applicability, and—especiallythe desalinated ones (S′)—by the low content of by-products in thebackwater of the production of brightened paper or board. They are alsoof optimum compatibility with with other usual additives conventionallyemployed in the production of the cellulosic substrate, especially paperand board.

[0068] In the following examples parts and percentages are by weight andthe temperatures are indicated in degrees Celsius. The employed startingoptical brighteners are of the following formulae:

[0069] Optical Brightener (A1) of the Formula

[0070] Optical Brightener (B1) of the Formula

EXAMPLE 1

[0071] a) 1000 g of an aqueous solution of Optical Brightener (A1)containing 0.2844 mol of (A1) per kg, and

[0072] 56 g of triethanolamine of 98% strength

[0073]  are mixed together and warmed to 60° C. To this is added over 20min a solution of

[0074] 22.4 g aqueous 30% HCl solution in

[0075] 200 g demineralized water.

[0076]  Further heating is applied to 80-85° C. with stirring until asolution forms. Cooling is applied to 35° C. and the mixture left tostand 30 minutes without stirring and the lower organic layer isseparated off. This is formulated to a concentration of 0.2844 mol/kgand 7% triethanolamine.

[0077] The obtained solution (SA2) contains the optical brightener (A2)which in the form of the free acid corresponds to the formula

[0078] and is in the form of the mixed sodium and triethanolammoniumsalt.

[0079] Yield approximately 960-985 g

[0080] The separation technique reduces the sodium ion concentrationfrom 1.45% of the original solution to 0.6-0.9% in the final liquid. Thetheoretical Na-ion concentration value for the half sodium halftriethanolammonium salt form is 0.56%. The sodium content in theoriginal solution is higher than theory, due to residual NaCl producedduring synthesis. The chloride content is similarly reduced from ca. 1%to typically 0.2-0.3%.

[0081] b) A second separation is carried out as above but using theOptical Brightener (B I) at a concentration of 0.2844 mol/kg. Theobtained solution (SB2) contains the optical brightener (B2) which inthe form of the free acid corresponds to the formula

[0082]  and is in the form of the mixed sodium and triethanolammoniumsalt.

[0083] c) Finally equal weights of the two formulated liquids (SA2) and(SB2) are mixed together to give a clear light brownish solution (S I)which is stable to the following

[0084] Stable upon cooling down to 2° C.—stays clear, doesn't separate

[0085] Stable to being stored with crystal seeds at 2° C. for at least 2weeks, 3 months or more

[0086] Stable to being frozen 3 days and then thawed out to give ahomogenous clear liquid once more

[0087] The stability of the mixture (WI) in the form of its solution(S1) in various proportions is superior to the stability of either ofthe two separate components (SA2) and (SB2). 50:50 (i.e. equimolar)mixtures are preferable but also 70:30 [=solution (S2)] and 30:70[=solution (S3)] are stable.

[0088] A product (S4) of further improved stability is obtained byadding water and triethanolamine to a total optical brightenerconcentration of 0.2275 mol/kg and a total triethanolamine concentrationof 7% (including the one in triethanolammonium salt form in the opticalbrightener mixture).

[0089] Other additives 0.5%-2% of the following also improve stability.

[0090] Mono-, di- or triethylene glycol, poly(ethyleneglycol)s (M_(w)200, 400, 600, 1000, or 1500), triethanolamine, triisopropanolamine,tris(hydroxymethyl)aminomethane, and2,2-bis-(hydroxymethyl)-2,2′,2″-nitrilotriethanol.

[0091] Trace amounts (0.5% or less) of other bases can also be added toraise the pH slightly from 8-8.5 to 9-9.5. The following bases may beused ammonia solution, NaOH, LiOH, KOH, mono-ethanolamine,diethanolamine.

[0092] Other mineral acids can also be used in the separation. Replacingthe 22.4 g of the 30% HCl with the following has been shown also producestable liquids: 9.0 g phosphoric acid (98%), or 12.95 g sulphuric acid(98%), or 21.0 g nitric acid (70%).

EXAMPLE 2

[0093] 500 g Optical Brightener (A1) solution (=0.1422 mol) and

[0094] 56 g triethanolamine 98% are mixed together and warmed to 60° C.

[0095]  To this is added over 20 minutes a solution of

[0096] 22.4 g of aqueous 30% HCl in

[0097] 200 g demineralized water. This can be left stirring warm 60° C.for an extended period (18 hrs+) without detriment to the final liquid.To this is added over 20 min

[0098] 500 g Optical Brightener (B I) solution (=0.1422 mol), andheating is applied to 80-85° C. with stirring until a solution forms.Cooling is applied to 35° C. and the mixture left to stand 30 minutesand the lower organic layer is separated off. The separated liquid isformulated to 0.2844 mol/kg and 7% total triethanolamine.

[0099] Yield approximately 960-985 g of Solution (S5).

[0100] The additives and bases mentioned in Example 1 can be used toimprove stability further. The different mineral acids can also be used.

[0101] The process may alternatively be carried out by using only halfthe triethanolamine and HCl for (A1), then adding the other half of thetriethanolamine, then the (B1) solution and then the other half of theacid.

EXAMPLE 3

[0102] a) 34.6 g of aqueous 30% HCl solution 350 g ice

[0103] 450 g demineralized water are mixed together and to this is addedslowly over ca. 20 min

[0104] 1000 g Optical Brightener (A1) solution (=0.2844 mol) preheatedto 60° C.

[0105]  A thick but stirrable slurry forms and the temperature reachesca 20° C. To this is now added

[0106] 50.6 g triethanolamine.

[0107]  And heating is applied to achieve a solution at ca 45-50° C. Oncooling again to 20° C. 2 layers form. The mixture is left to stand 30minutes and the lower organic layer separated off. This is formulated toa concentration of 0.2844 mol/kg and 7% total triethanolamine.

[0108] Yield approximately 960-985 g.

[0109] If the slurry formed becomes too thick to stir, some (half) ofthe 50.6 g of triethanolamine can be added half way through the additionof the 1000 g of optical brightener (A1) solution with no detriment.

[0110] b) The same process is carried out for the Optical Brightener (BI) and

[0111] c) the two products of a) and b) are mixed in equal proportionsto give Solution (S6).

[0112] Alternatively, instead of 1000 g of the optical brightener (A1)solution, first 500 g of the Optical Brightener (A1) solution and then500 g of the Optical Brightener (B1) solution are added and then the twoare separated together, analogously as described in Example 3a), to giveSolution (S7).

[0113] Alternatively all or half of the acid may be put in at thebeginning.

[0114] Again the different acids, additives and bases listed above inExample 1 can be used.

EXAMPLE 4

[0115] a) 34.6 g aqueous HCl solution (30%)

[0116] 350 g ice

[0117] 450 g demineralized water are mixed together and to this is addedslowly over ca. 20 min

[0118] 1000 g Optical Brightener (A1) solution of concentration 0.2844mol/kg is preheated to 60° C. A thick but stirrable slurry forms and thetemperature reaches ca 20° C. This is filtered and the presscake washedwith cold water acidified to pH 1 with a minimum of HCl. The presscakeis pressed as dry as possible in the filter and then redissolved in

[0119] 400 g demineralized water and

[0120] 50.6 g triethanolamine. Heating is applied to achieve a solutionat ca 50° C. This is formulated to 0.2844 mol/kg and 7% totaltriethanolamine.

[0121] Yield approx. 960-985 g

[0122] b) The same process is carried out for the Optical Brightener (BI) and

[0123] c) the two products are mixed in equal proportions to giveSolution (S8).

[0124] Again the different acids, additives and bases stated in theabove Examples can be used.

[0125] Similarly 500 g of the Optical Brightener (A1) solution and then500 g of the Optical Brightener (B1) solution are added and then the twoare isolated and formulated together analogously to Example 4a) to giveSolution (S9).

EXAMPLE 5

[0126] a) 1198 g demineralized water

[0127] 107.9 g triethanolamine and

[0128] 86.3 g aqueous 30% HCl are mixed together.

[0129]  This exotherms to ca. 28° C. and is further heated to 35° C. Tothis is added slowly over ca. 20 min

[0130] 1000 g Optical Brightener (A1) solution (=0.2844 mol) preheatedto 60° C. A soft precipitate initially forms which melts to form anemulsion as the temperature reaches ca 42° C., the final temperaturereached being about 45° C. This is stirred at 45° C. for 1 hour thenstood for 90 minutes without stirring at 45° C.

[0131] This is formulated to 0.2844 mol/kg and 7% total triethanolamine.

[0132] Yield approximately 960-985 g.

[0133] b) The same process is carried out for the Optical Brightener(B1) and

[0134] c) the two mixed in equal proportions to give Solution (S10).

[0135] Again the different acids, additives and bases stated in theabove Examples can be used.

[0136] Similarly 500 g of the Optical Brightener (A1) solution and then500 g of the Optical Brightener (B1) solution are added and then the two(A2) and (B2) are separated together and formulated together analogouslyto Example 5a) to give Solution (S11).

EXAMPLE 6

[0137] 1000 g demineralized water

[0138] 1000 g Optical Brightener (A1) solution (=0.2844 mol) and

[0139] 1000 g Optical Brightener (B1) solution (=0.2844 mol) are mixedtogether and heated to 50° C.

[0140]  This is ultrafiltered through a membrane over ca. 8 hours with apermeation rate of about 1 litre/hour. A solution of

[0141] 53.0 g triethanolamine and

[0142] 43.1 g of HCl solution of 30% strength in

[0143] 660 g demineralized water is slowly added during this time.

[0144]  As the triethanolamine hydrochloride solution is added theOptical Brightener mixture temporarily precipitates but rapidlydissolves. If the Optical Brightener mixture stays out of solution, thena minimum amount of triethanolamine can be added. Also during the 8hours as the total volume is kept constant with more water. The sodiumcontent and the chloride content are monitored—when sodium ion contentis 0.6% or less and the chloride ion content 0.1-0.2%, the volume isallowed to reduce to 1750 ml.

[0145] The obtained product is formulated to an optical brightenerconcentration of 0.2844 mol/kg and 7% total triethanolamine.

[0146] Yield approximately 1860-1930 g of Solution (S 12).

[0147] The same process can be carried out for each of the two OpticalBrighteners (A1) and (B1) separately and then (A2) and (B2) in the formof the produced solutions can be mixed afterwards [=Solution (S13)].

[0148] Again the different acids, additives and bases noted above can beused.

EXAMPLE 7

[0149] To 8333 g of an aqueous solution of 1 mole of the compound offormula

[0150] at 60° C. is added 1.75 mole of diethanolamine (208.8 g of an 88%solution in water) and then 1.75 mole of amine of formula

[0151] (321 g of a 72% solution in water). The mixture is heated toreflux and maintained at reflux for 4 hours, while controlling the pH to8.5-9.0 with the addition of minimal amounts of NaOH. An oil forms asthe reaction proceeds. 44.3 g of sodium chloride is added, and themixture is stirred for 10 minutes and then cooled to 90° C. with slowagitation (the agitation is sufficiently slow to prevent aeration andflotation of the oil). Stirring is stopped and the mixture is allowed tostand for 10 minutes. Two layers form and the lower organic layer isseparated from the top, salt containing, aqueous layer and made to0.2844 mol/kg and kept at 60° C. Yield approximately 3300-3500 kg.

[0152] Following the conditions laid out in Example 5, a secondseparation is carried out. In a separate vessel is mixed 4193 g ofdemineralized water, 377.7 g of triethanolamine and 302.0 g of 30%hydrochloric acid. As before an exotherm heats the mixture to ca. 28° C.and heating is applied to reach 35° C. The solution from the first stageat 60° C. is added slowly to this and as before the temperature slowlyrises to about 42° C. at the end of the addition. Further heating isapplied with slow stirring so that the optical brightener melts andforms an emulsion. Stirring is continued for 1 hour, then it is stoppedand the mixture is allowed to stand for 90 minutes and the oil phase isseparated. The oil is formulated as before to an optical brightenermixture concentration of 0.2844 mol/kg and 7% of total triethanolamine.Yield approximately 3300-3400 g of Solution (S14).

[0153] The formed optical brightener mixture is a mixture of the twooptical brighteners (A2) and (B2) and a third new asymmetrical species(C2) which in the form of the free acid corresponds to the formula

[0154] and is obtained in the mixed sodium/triethanolammonium salt form.

EXAMPLE 8

[0155] Here each of the optical brighteners (A2) and (B2) is synthetisedseparately by reaction of the intermediate of formula (VI′) with theamine of formula (IV′) and with diethanolamine, in the presence oftriethanolamine.

[0156] a) For 1 mole of Optical Brightener (A1) solution (3.52 kg ofsolution), 0.75 mole of triethanolamine (112 g) is required for theformation of enough triethanolamine-HCl in situ during the condensationreaction. A minimum amount of added NaCl encourages two layers to form.The separation is carried out at 30° C. Some triethanolamine-HCl (abouta quarter of it) is lost in the aqueous layer.

[0157] b) Optical Brightener (B1) is processed analogously.

[0158] c) The two separated bottom organic layers are mixed with eachother and the mixture is formulated to a total optical brightenermixture concentration of 0.2844 mol/kg and 7% total triethanolamine togive Solution (S15).

[0159] The other additives and pH adjusting bases are preferred in theseformulations since only one separation is carried out for eachbrightener.

[0160] Application Example A

[0161] 200 g of a pulp suspension (2.5% aqueous suspension of a 50%mixture of bleached soft wood and hard wood pulps beaten to a freenessof about 20°SR) is measured into a beaker and stirred, 40% fillersuspension (80 g of 100 g/litre calcium carbonate suspension in water)is added (typically Snowcall 60 from Croxton and Garry Ltd.). Thesuspension is stirred for one minute and p % of the first product ofExample 1, i.e. of Solution (S1), is added (p=0, 0.1, 0.2, 0.4, 0.8, 1,1.4, 1.8 and 2; p % being related to the dry pulp and p=0 representingthe blank). After the addition the mixture is stirred for a further 0.5minutes and then 1.7% (3.4 g) of neutral size is added (typically adispersion of 2.5 g of Aquapel 360×in water—Aquapel 360×is analkyl-ketene dimer size suspension from Hercules Ltd.). After theaddition of the size a retention aid may be added—typically CartaretinPC. The mixture is then diluted to one litre and the paper sheet isformed on a laboratory sheet former (basically this is a cylinder with awire gauze at the bottom—the cylinder is partly filled with water, thepulp suspension is added, air is then blown through to ensure the pulpis well dispersed, a vacuum is then applied and the pulp slurry ispulled through the wire to leave a paper sheet, this sheet is removedfrom the wire and pressed and dried). The sheet is left in a humiditycabinet to achieve equlibrium and then the whiteness is measured using aDatacolor ELREPHO 2000 spectrophotometer. The measured values show thatwith the optical brightener mixture a high whiteness degree and yield isachieved. The COD and nitrogen content of the backwater are very low.

[0162] Application Example B

[0163] 200 g of a pulp suspension (2.5% aqueous suspension of a 50%mixture of bleached soft wood and hard wood pulps beaten to a freenessof about 20°SR) is measured into a beaker and stirred and 20% fillersuspension (40 g of 100 g/litre china clay suspension in water) is added(typically China Clay grade B from EEC Ltd.). The suspension is stirredfor one minute and p % of the first product of Example 1, i.e. ofSolution (S1), is added (p=0, 0.1, 0.2, 0.4, 0.8, 1, 1.4, 1.8 and 2; p %being related to the dry pulp and p=0 representing the blank). After theaddition the mixture is stirred for a further 5 minutes and then 2% ofrosin size solution is added (typically “T size 22/30” from Hercules),the mixture is stirred for a further 2 minutes and then 3 ml of alumsolution (50 g alum in 1 litre water) are added and the mixture isstirred for a further 2 minutes. The mixture is then diluted to onelitre and the paper sheet is formed on a laboratory sheet former. Thesheet is left in a humidity cabinet to achieve equlibrium and then thewhiteness is measured using a Datacolor ELREPHO 2000 Spectrophotometer.The measured values show The measured values show that with the opticalbrightener mixture a high whiteness degree and yield is achieved. TheCOD and nitrogen content of the backwater are very low.

[0164] Application Example C

[0165] A coating composition is prepared containing 3000 parts chalk(fine, white, high purity calcium carbonate with a density by ISO 787/10of 2.7, commercially available under the trade name HYDROCARB OG ofPlüss-Stauffer AG, Oftringen, Switzerland), 1932 parts water, 18 partscationic dispersing agent, and 600 parts latex (a copolymer of n-butylacrylate and styrene latex of pH 7.5-8.5, commercially available underthe trade name ACRONAL S320D). A predetermined amount of the firstproduct of Example 1, i.e. of Solution (St), (0, 0.313, 0.625, 0.938,1.25 and 1.875 mmol/kg referred to the optical brightener mixture) isadded with stirring to the coating composition, and the solids contentis adjusted to 55% by the addition of water. The so prepared coatingcomposition is then applied to a commercial 75 g/m2 neutral-sized (withconventional alkyl ketene dimer), bleached paper base sheet, using anautomatic wire-wound bar applicator with a standard speed setting and astandard load on the bar. The coated paper is dried for 5 minutes at 70°C. in a hot air flow. The dried paper is allowed to condition, thenmeasured for CIE whiteness on a calibrated Datacolor ELREPHO 2000spectrophotometer. The measured values show that with the opticalbrightener mixture a high whiteness degree and yield is achieved.

[0166] Analogously as the first product of Example 1 or Solution (S1),equivalent amounts of the further products of Example 1 and of theproducts of each of Examples 2-8 [in the form of Solutions (S2) to(S15)] and of the modified formulations of each of Examples 1-8 areemployed in Application Examples A, B and C.

1. An optical brightener mixture (W) comprising an optical brightener(A) of formula

wherein R signifies hydrogen or methyl, R1 signifies hydrogen,unsubstituted C₁₋₆-alkyl, C₁₋₆-alkyl substituted with carbamoyl orcarboxy, C₂₋₆-alkyl substituted with hydroxy or methoxy, hydroxy- ormethoxy-(C₂₋₃-alkoxy)-(C₂₋₃-alkyl) R₂ signifies C₁₋₆-alkyl substitutedwith carbamoyl or carboxy, or R₁ and R₂ together with the nitrogen towhich they are linked form a carboxypyrrolidine ring, and M signifies anequivalent of a cation, and an optical brightener (B) of formula

wherein R signifies hydrogen or methyl, R₃ signifies hydrogen,unsubstituted C₁₋₆-alkyl, C₂₋₆-alkyl substituted with hydroxy ormethoxy, or hydroxy- or methoxy-(C₂₋₃-alkoxy)-(C₂₋₃-alkyl), R4 signifieshydrogen, unsubstituted C₁-alkyl, C₂₋₆-alkyl substituted with hydroxy ormethoxy, or hydroxy- or methoxy-(C₂₋₃-alkoxy)-(C₂₋₃-alkyl), or R₃ and R4together with the nitrogen to which they are linked form a morpholinering, and M signifies an equivalent of a cation.
 2. A process for theproduction of a mixture (W) according to claim 1, wherein (A) is mixedwith (B) optionally in the presence of water or a compound of formula

 in which Hal signifies halogen and M′ signifies an alkali metal cation,is reacted with a mixture of amines of formulae

and

by which a mixture of the compounds (A) and (B) of formulae (Ia) and(Ib) with a comound (C) of formula

is formed.
 3. An optical brightener (C) of formula (Ic) as defined inclaim
 2. 4. A mixture (W) according to claim 1, which is a mixture of(A) and (B) or of (A), (B) and (C), where (C) is as defined in claim 2or
 3. 5. A mixture (W) of optical brighteners (A) and (B) according toclaim 1 or 4, wherein the cations in the significance of M are selectedfrom M₁ alkali metal cations and unsubstituted ammonium and M₂ ammoniummono-, di- or trisubstituted with C4-alkyl and/or C₂₋₃-hydroxyalkyl. 6.A mixture (W) according to claim 4 or 5, wherein cations M₁ and M₂ areboth present as M in the mixture.
 7. An aqueous concentrated composition(S) of an optical brightener mixture (W) according to any one of claims1 or 4 to
 6. 8. An aqueous composition (S) according to claim 7, whichis a concentrated solution (S′) in which the content of electrolytesother than those involved in salt formation in (A), (B) and—ifpresent—(C), is less than 5% by weight referred to the weight of (W). 9.A process for the production of a solution (S′) according to claim 8,wherein a) a salt-containing solution (S″) of (W) is desalinated bymembrane filtration or b) the mixture (W) is precipitated in acid formby acidification of a salt-containing aqueous solution (S″) of (W) witha strong mineral acid, separated and redissolved in salt form byreaction with the suitable base or base mixture or c) the (W) solution(S″) is treated with an acid ion exchange resin or acid membrane in thepresence of amine as suitable for introducing M₂, or d) thesalt-containing mixture (W) is selectively separated in a system of twoliquid phases L₁ and L₂, of which L₁ is aqueous and dissolves theextraneous electrolytes and L₂ is organic and contains (W) and maycontain a minor proportion of dissolved water, and the desalinated (W)containing phase L₂ is separated from the salt-containing aqueous phaseL₁, or the salt-containing mixture (W) is selectively dissolved in asystem of two immiscible solvents and the desalinated (W)-containingphase is separated from the salt-containing phase or two or more of thestated process variants a), b), c) and d) are combined.
 10. A processfor the production of a desalinated dry mixture (W) according to any oneof claims 1 or 4 to 6, wherein a desalinated solution (S′) producedaccording to claim 9 is dried to a powder or granulate.
 11. An aqueousconcentrated composition (S) according to claim 7 or 8 furthercontaining one or more formulation additives (F).
 12. An aqueousconcentrated composition (S) according to claim 11, wherein (F) isselected from (F₁) a stabilising additive, (F₂) a defoamer, and/or (F₃)an additive for protection against the damaging action ofmicroorganisms.
 13. Use of a mixture (W) according to any one of claims1 or 4 to 6, optionally in the form of an aqueous concentratedcomposition (S) according to any one of claims 7, 8 or 12, for opticallybrightening a substrate brightenable with anionic optical brighteners.14. Use according to claim 13, for the optical brightening of cellulosicsubstrates.
 15. Use according to claim 14, for the optical brighteningof paper.